1. Field of the Invention
The invention relates to composition of piezoelectric porcelain for ceramic piezoelectric sensor to be used for detecting vibration, and in particular to the composition of piezoelectric porcelain suited for detecting vibration of automobile engines.
2. Description of the Related Art
When the composition of piezoelectric porcelain is used to the piezoelectric ceramic sensor to be used for detecting vibration, it is required to have as characteristics high electromechanical coupling factor kt of longitudinal vibration in thickness (for example, 50% or higher) and large specific dielectric constant (for example, 1000 or more).
For stabilizing sensitivity of the sensor to changes of environmental temperature, it is preferable that change of the piezoelectric characteristics such as electromechanical coupling factor, capacitance and others is small irrespectively of changes in the temperature (for example, in a case of the electromechanical coupling factor, the electromechanical coupling factor is xe2x88x92100 ppm/xc2x0 C. to 100 ppm/xc2x0 C. when the temperature is changed in the range between xe2x88x9240xc2x0 C. to 85xc2x0 C.).
Further, depending on usage, the sensor itself is often effected with pressure, otherwise since engines and the neighborhood thereabout are necessarily actuated under large vibration, strength is demanded to be high as possible.
Composition of lead titanate zirconate base has conventionally been known as suited for the composition of piezoelectric porcelain to be used to ceramic oscillators or ceramic filters, and it has been variously improved in response to usage.
There are known, for example, a material where oxides of Nb, Sb, W, Mn and the like are added to the composition of lead titanate zirconate base to improve porcelain properties, another material where composite perovskite compound such as Pb(Nbxc2xdSbxc2xd)O3 and Pb(Mg⅓Nb⅔)O3 as a third component is made solid solution in the composition of lead titanate zirconate base to improve the porcelain properties-and further oxides of Nb, Sb, W, Mn are added, or a further material where a part of Pb of these above compositions is substituted with Ba, Sr or Ca for improving the temperature characteristics of resonance frequency.
Applicant previously proposed that pyrochlore typed composite oxide of Pb2Sb2O7, Ba2Sb2O7 or others is made solid solution as a third component in a base porcelain composition of lead titanate zirconate, thereby enabling to obtain large electromechanical coupling factor kp and specific dielectric constant ∈, and small change of capacitance owing to changes in the temperature (JP-B-54-26716 and JP-B-54-26717).
Further, the applicant previously proposed that the pyrochlore typed composite oxide of Ba2Sb2O7 is made solid solution as a third component in the base porcelain composition of lead titanate zirconate, to which Nb2O5 is added as a sub component, thereby enabling to obtain large electromechanical coupling factor kt and specific dielectric constant ∈, and small temperature characteristic of electromechanical coupling factor kt (JP-A-50-156700).
Since the conventionally known composition of the piezoelectric porcelain aimed at merely making the specific dielectric constant and the electromechanical coupling factor large as the piezoelectric ceramics to be used to actuators, even if the longitudinal electromechanical coupling factor kt in thickness and specific dielectric constant ∈ were large, there was a problem in that change of the piezoelectric characteristics was large corresponding to change of temperature.
JP-B-54-26716 and JP-B-54-26717 propose an addition of MnO2 as a technique for increasing a mechanical strength, but a problem is that this technique makes the mechanical quality factor Qm large, and a product cannot be applied to this kind of sensors.
In addition, JP-A-50-156700 shows the good piezoelectric characteristics and temperature characteristic for a piezoelectric sensor, but a problem exists in the mechanical strength, and a product cannot be employed to the piezoelectric sensors to be used under large vibration.
Accordingly, it is an object to provide such composition of piezoelectric porcelain having the large specific dielectric constant and electromechanical coupling factor, and the small change of the piezoelectric characteristic owing to changes in the temperature and mechanical quality factor Qm, and the large strength.
As means for solving these problems, the invention is to disclose the following structures.
(1): A composition of piezoelectric porcelain is composed as x(Pb2Sb2O7)xc2xd. (1xe2x88x92x)[Pba(ZryTiz)O3] (provided that 0.98xe2x89xa6axe2x89xa60.999, 0.005xe2x89xa6xxe2x89xa60.05, 0.50xe2x89xa6yxe2x89xa60.54, 0.46xe2x89xa6zxe2x89xa60.50, y+z=1) is a main component, and to the weight of 1 mol of the main component, 0.1 to 1.0 wt % of at least one kind of W, Sb, Nb, and Ta in terms of WO3, Sb2O3, Nb2O5, and Ta2O5 is added as a sub component, and 0.01 to 0.1 wt % of Si in terms of SiO2 is added as a further sub component.
(2): A composition of piezoelectric porcelain is composed as x(Me2Sb2O7)xc2xd. (1xe2x88x92x)[Pba(ZryTi2)O3] (provided that 0.98xe2x89xa6axe2x89xa60.999, 0.005xe2x89xa6xxe2x89xa60.05, 0.50xe2x89xa6yxe2x89xa60.54, 0.46xe2x89xa6zxe2x89xa60.50, y+z=1, Me is at least one kind selected from Ba and Sr) is a main component, and to the weight of 1 mol of the main component, 0.1 to 1.0 wt % at least one kind of W, Sb, Nb, and Ta in terms of WO3, Sb2O3, Nb2O5, and Ta2O5 is added as a sub component, and 0.01 to 0.1 wt % of Si in terms of SiO2 is added as a further sub component.
By this structure, it is possible to obtain the composition of piezoelectric porcelain for the piezoelectric sensor having the excellent sensitivity and temperature characteristic and the high reliability in strength of the piezoelectric porcelain.
The pyrochlore typed composite oxide Pb2Sn2O7 or Me2Sb2O7 (Me is at least one kind selected from Ba and Sr) is made solid solution as the third component in the base porcelain composition of lead titanate zirconate because of improving the characteristics of the piezoelectric porcelain. It is possible thereby to obtain the composition of piezoelectric porcelain suited to the piezoelectric sensor for detecting vibration in the ratio of Ti/Zr in a relatively broad range.
To the weight of 1 mol of the main component, 0.1 to 1.0 wt % of at least one kind of W, Sb, Nb, and Ta in terms of WO3, Sb2O3, Nb2O5, and Ta2O5 is added as a sub component, because of making crystal grain diameter of porcelain fine so as to improve the stability of the piezoelectric porcelain and making change of the piezoelectric characteristic owing to changes in the temperature small. It is possible thereby to obtain the piezoelectric porcelain for the piezoelectric sensor having small change of the characteristics by temperature.
0.01 to 0.1 wt % of Si in terms of SiO2 is added as a further sub component to the weight of 1 mol of the main component, thereby enabling to make binding power large and heightening the strength of the piezoelectric porcelain large without deteriorating the characteristics of the piezoelectric porcelain.
If the ratio of the composition of Pb is rendered to be 0.98 to 0.999, the strength of an element may be more heightened.